1. Field of the Invention
The invention relates to an inter-vehicle distance control apparatus and an inter-vehicle distance control method. More specifically, the invention relates to an inter-vehicle distance control apparatus and an inter-vehicle distance control method that control a distance between a vehicle and a first preceding vehicle ahead of the vehicle, by controlling drive power and braking power of the vehicle.
2. Description of the Related Art
Vehicles provided with Adaptive Cruise Control (ACC) systems have been put into practical use. The ACC systems maintain a distance between a host vehicle and a vehicle ahead of the host vehicle (hereinafter, the vehicle ahead of the host vehicle will be referred to as “first preceding vehicle”), or the speed of the host vehicle by automatically controlling drive power and braking power of the host vehicle. The ACC systems are classified into a low speed range ACC system, a high speed range ACC system, and a full speed range ACC system, according to a speed range in which the host vehicle is controlled, and a control method.
For example, the high speed range ACC system controls the host vehicle so that when there is the first preceding vehicle ahead of the host vehicle, the host vehicle travels in a high speed range and follows the first preceding vehicle while the distance between the host vehicle and the first preceding vehicle is maintained at a preset inter-vehicle distance, and when there is no first preceding vehicle ahead of the host vehicle, the host vehicle constantly travels at a preset upper limit speed. The low speed range ACC system controls the host vehicle so that when there is the first preceding vehicle ahead of the host vehicle, the host vehicle travels in a low speed range, and follows the first preceding vehicle while the distance between the host vehicle and the first preceding vehicle is maintained at a preset inter-vehicle distance, and when there is no first preceding vehicle ahead of the host vehicle, a vehicle-following control for following the first preceding vehicle is stopped. The full speed range ACC system controls the host vehicle so that when there is the first preceding vehicle ahead of the host vehicle, the host vehicle follows the first preceding vehicle while the distance between the host vehicle and the first preceding vehicle is maintained at an inter-vehicle distance set for each speed in an entire vehicle speed range, and when there is no first preceding vehicle ahead of the host vehicle, the host vehicle constantly travels at a preset vehicle speed. Thus, the full speed range ACC system seamlessly controls the host vehicle in the entire vehicle speed range from the low speed range to the high speed range.
Japanese Patent Application Publication No. 2005-231490 (JP-A-2005-231490) describes a vehicle-following control apparatus that includes the ACC system. The vehicle-following control apparatus described in the publication No. 2005-231490 sets a target stop position for the host vehicle, based on a positional relation between the host vehicle provided with the vehicle-following control apparatus and the first preceding vehicle, and executes a stop control. Also, the vehicle-following control apparatus described in the publication No. 2005-231490 changes the control from the stop control to the vehicle-following control for following the first preceding vehicle, when a vehicle ahead of the first preceding vehicle (hereinafter, the vehicle ahead of the first preceding vehicle will be referred to as “second preceding vehicle”) starts moving while the host vehicle is stopped.
If the second preceding vehicle suddenly stops or the second preceding vehicle is stopped while the host vehicle and the first preceding vehicle are traveling, the first preceding vehicle may suddenly stop, or may avoid the second preceding vehicle by steering, to avoid a collision with the second preceding vehicle. However, the vehicle-following control apparatus described in the publication No. 2005-231490 does not take into account the possibility that the first preceding vehicle may be in the above-described situation. Therefore, it is difficult for the vehicle-following control apparatus to appropriately control the travel of the host vehicle when the above-described situation occurs. Also, when the vehicle-following control is executed so that the host vehicle follows the first preceding vehicle while the distance between the host vehicle and the first preceding vehicle is maintained, the stopped second preceding vehicle is not generally taken into account. Therefore, the vehicle-following control apparatus may not be able to appropriately control the host vehicle when the second preceding vehicle is stopped.